Gliclazide works by forcing your pancreas to release extra natural insulin. If this extra natural insulin happens to be enough to deal with the glucose in your bloodstream, injecting more insulin will make you go too low. It sounds to me like you don't need both Glic and injected insulin, which maybe why your doctor took you off the insulin. Your body was ending up with too much.
If the Glic isn't working for you, and/or it is making you ill, you need to go back to your doctor and discuss it all with him. See your GP and take along a record of your most recent blood sugar levels to show him.